Most passenger transportation vehicles comprise a grey water system and a waste water system. Therein, grey water may be used water from drinking water systems and washing basins. Waste water, also denoted as black water, may be contaminated water such as toilet waste water and sewage.
Usually the grey water system and the waste system are designed as separate independent systems. While the waste water system is adapted for accumulating and storing waste water in a waste water tank, the grey water system is adapted for discharging the grey water outside the vehicle. In case of aircrafts the grey water has to be drained overboard without building ice formations at the aircraft fuselage in case of low temperatures. For this purpose heated draining masts may be provided at the vehicle.
Alternatively, the grey water may be released into the waste water tank. However, an additional transfer unit with security valves is necessary at the connection of the grey water and the waste water systems for preventing waste water from flowing back to galleys and basins. Such a transfer unit is known for example from DE 10 2005 045 343 A1 or US 2007 0 068 575 A1.